When we say "pyrometallurgy", we mean the metallurgical process used to separate and recover metals. The furnaces that are used in this process produce sludge and dust. Until now, however, they were simply dumped in landfills. This is absurd on two counts! Why? Because landfilling is not only expensive but also has a significant impact on the environment; and above all, these tailings still contain a lot of manganese! It is thus a waste of value and a way of squandering raw material. The objective of the Go-4-0 project is thus to recover this sludge and dust to produce an optimal blend; this new reusable material is then pelletized in the form of briquettes and sent back into the furnaces. The manganese lost as smoke or sludge during the pyrometallurgical process is thus recycled.
Go-4-0 has brought together a consortium of six partners, including manufacturers, SMEs, academics and research centers. It began in July 2016 and finished at the end of December 2019. Nearly 98% of its €2,5m budget was financed by EIT-Raw Materials, an institution of the European Union. During this project, several pilots were carried out, specifically in order to manufacture the briquettes, but also to test their chemical composition and performance in a furnace during the normal course of a pyrometallurgical process. An entire PhD thesis was devoted to the manufacturing of these briquettes.
The challenge: to design the ideal briquette
The main difficulty in the manufacture of briquettes has involved the composition of the briquette and more particularly how to achieve the perfect blend of ingredients: sludge, dust, carbon and binder. If there is too much binder, it disrupts the furnace's thermal performance and adversely affects the smooth running and efficiency of the furnace. If there is not enough binder, the briquette crumbles during shipment or as soon as it is introduced into the furnace and immediately becomes dust or sludge again. Since the smooth operation of a furnace depends on a delicate balance between the different types of input raw materials, it is imperative that this balance not be upset. The second challenge of the project thus involved calculating as accurately as possible the ideal quantity of briquettes to be introduced into the furnace as raw material so as not to disturb the furnace's thermal equilibrium. Consequently, several tests were necessary to find the right ratio between the quantities of briquettes to be put into the kiln in relation to the other inputted raw materials.
Work performed during the project
The project was divided into a number of interlinked areas of focus:
- The first focus was to determine the ideal composition of the briquette, which needed to contain the right amounts of sludge, dust, carbon and the proper amount of the appropriate binder. The briquettes then had to be tested to determine their durability (to avoid crumbling in particular) and how they would age.
- The purpose of the second focus area was to check that the introduction of briquettes into the furnace did not disrupt the performance of the furnace, but also to understand the impact of the introduction of briquettes on the manganese reduction process.
- The third area of focus was more commercial in nature since it involved carrying out a market study on the benefits of this innovative circular economy solution.